In addition to good rigidity, chemical resistance, and impact resistance, acrylonitrile-butadiene-styrene (ABS) copolymers have relatively good physical properties, such as moldability and gloss. Therefore, ABS copolymers are widely used as housings or interior/exterior materials for various products, such as electrical/electronic parts, office equipment, and automobile parts.
In general, when an ABS copolymer having improved impact resistance is prepared, a diene rubber latex such as a butadiene rubber is graft-copolymerized with styrene and acrylonitrile using emulsion polymerization, and then the prepared copolymer is kneaded with a SAN resin, such as styrene-acrylonitrile copolymers, and a thermoplastic resin, such as polystyrene and polymethyl methacrylate, to prepare a resin composition.
However, when emulsion polymerization is performed, reactants, such as polymerization water, monomers, an emulsifier, an initiator, and a molecular weight modifier, are usually included. Since an excess of these reactants remains in a prepared latex after emulsion polymerization, thermal stability is lowered during thermoforming, resulting in discoloration of a final product and degradation of physical properties of the final product.